Liz Wager's recent blog in the BMJ discusss how tricky retractions can be, such as a recent one where the retraction was requested by the company who funded the study and whose employees carried out the research. Although there were some errors in the study, the conclusions were valid. (Liz Wager, Trouble with retractions,1 July: http://blogs.bmj.com/bmj/2013/07/01/liz-wager-trouble-with-retractions/)